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> Unfortunately, to get the last element we still have to do the clunky javaScriptArray[ javaScriptArray.length - 1 ] technique. This ... has always seemed like

> Unfortunately, to get the last element we still have to do the clunky javaScriptArray[ javaScriptArray.length - 1 ] technique. This ... has always seemed like a major oversight in the ECMAScript standard. Sort of an aside, but there's a stage 1 (relatively early) proposal to add an `array.lastItem` property that should finally improve things: https://github.com/keithamus/proposal-array-last https://github.com/keithamus/proposal-array-last

aidos 8y ago
I miss python’s list operators so much when I’m in JS (along with lots of other stuff). Is there a reason why we couldn’t use python’s x[-1] syntax in JS?
- alangpierce 8y ago
  There's probably existing code out there that relies on `arr[-1]` returning `undefined`, e.g. looping backward through an array until it gets a falsy value. You can also assign to `arr[-1]` and it'll work (it assigns to a new -1 key, not to the end of the array), and maybe some people do that in existing code. They had to pick `lastItem` as the name instead of just `last` since using `last` is also known to break the web. It's also not obvious that negative array accesses should behave that way. It's a tradeoff where it's more convenient in some cases but feels a bit less elegant and can lead to bugs (particularly dynamic array accesses that are accidentally negative). But FWIW, `slice` already implements this behavior, e.g. `arr.slice(-1)[0]` is a way to get the last element of an array, so there's certainly precedent in JS for it.
MarsAscendant 8y ago
In the list of useful functions I'd accumulated over a few years of JS, there are `[].last` and `[].lastIndex()`. The former is a property getter/setter implanted into the Array object¹. The latter is a function that returns `[].length - 1 || 0`. ¹ I know planting properties and functions directly onto the basic objects is generally frowned upon, but I see no harm in doing that for personal projects. Using it in the big-web production might be verboten, but it doesn't I can't make my coding life a bit easier. Meanwhile, I have a problem with the "web compatibility naming safeguard" argument over the names of the proposed properties/functions. Surely, the websites using `[].last` override the namespace to begin with. If, say, `[].last` were to be accepted, how could it break the sites using the override version? Outside of that, the fact that new proposals have to cow before a widespread conventional use of the names renders me confused. I feel like the JS engine should take priority over mere convention. Sure, some websites might be hurt in the process, but at least the generations of current and future coders would have few problems figuring out what the new functions do. Exhibit 1: `globalThis`. Nuff said? Exhibit 2: `[].smoosh`, which apparently was in the books [https://github.com/staltz/prevent-smoosh https://github.com/staltz/prevent-smoosh]. No longer is: it's now `[].flat`. Exhibit 3: `Math.clamp()`, in questions [https://github.com/rwaldron/proposal-math-extensions#questions https://github.com/rwaldron/proposal-math-extensions#questio...] for the `Math` extension proposal. (Yet undecided-upon.) `[].last` just makes sense.

aidos 8y ago

I miss python’s list operators so much when I’m in JS (along with lots of other stuff). Is there a reason why we couldn’t use python’s x[-1] syntax in JS?

alangpierce 8y ago
There's probably existing code out there that relies on `arr[-1]` returning `undefined`, e.g. looping backward through an array until it gets a falsy value. You can also assign to `arr[-1]` and it'll work (it assigns to a new -1 key, not to the end of the array), and maybe some people do that in existing code. They had to pick `lastItem` as the name instead of just `last` since using `last` is also known to break the web. It's also not obvious that negative array accesses should behave that way. It's a tradeoff where it's more convenient in some cases but feels a bit less elegant and can lead to bugs (particularly dynamic array accesses that are accidentally negative). But FWIW, `slice` already implements this behavior, e.g. `arr.slice(-1)[0]` is a way to get the last element of an array, so there's certainly precedent in JS for it.

MarsAscendant 8y ago

In the list of useful functions I'd accumulated over a few years of JS, there are `[].last` and `[].lastIndex()`. The former is a property getter/setter implanted into the Array object¹. The latter is a function that returns `[].length - 1 || 0`. ¹ I know planting properties and functions directly onto the basic objects is generally frowned upon, but I see no harm in doing that for personal projects. Using it in the big-web production might be verboten, but it doesn't I can't make my coding life a bit easier. Meanwhile, I have a problem with the "web compatibility naming safeguard" argument over the names of the proposed properties/functions. Surely, the websites using `[].last` override the namespace to begin with. If, say, `[].last` were to be accepted, how could it break the sites using the override version? Outside of that, the fact that new proposals have to cow before a widespread conventional use of the names renders me confused. I feel like the JS engine should take priority over mere convention. Sure, some websites might be hurt in the process, but at least the generations of current and future coders would have few problems figuring out what the new functions do. Exhibit 1: `globalThis`. Nuff said? Exhibit 2: `[].smoosh`, which apparently was in the books [https://github.com/staltz/prevent-smoosh https://github.com/staltz/prevent-smoosh]. No longer is: it's now `[].flat`. Exhibit 3: `Math.clamp()`, in questions [https://github.com/rwaldron/proposal-math-extensions#questions https://github.com/rwaldron/proposal-math-extensions#questio...] for the `Math` extension proposal. (Yet undecided-upon.) `[].last` just makes sense.